Various methods are known which attempt to block the passage of fluids from a subterranean formation into a communicating wellbore. The subterranean formation may be of any type, such as a heavy oil or gas producing reservoir, and the fluids may be desired to be blocked or their flow impeded for various reasons.
For instance, hydrocarbon producing wells, i.e. those producing oil or natural gas, may also produce an amount of water due to an influx of water into the wellbore. Over time, the amount or percentage of produced water may increase resulting in a corresponding decrease in the production of the desired hydrocarbons, eventually rendering further production of hydrocarbons from the well uneconomical.
Further, gas production from water drive reservoirs often suffers from excessive water production. In this instance, the influx of water into the gas well requires the gas to lift the water from the bottom of the wellbore to the surface. As the water influx increases, the pressure gradient required to lift the water up the wellbore also increases. This causes a decrease in gas flux from the reservoir into the wellbore. As a result, gas production decreases and eventually the gas well stops flowing.
As a result, various remedial measures have been developed to attempt to block the flow of water into the wellbore or otherwise abate the water influx. For instance, the passage of undesirable fluids, such as water, may be blocked from passage into the wellbore from the formation by the placement of a chemical blocking agent in the formation or reservoir. In this case, the presence of the chemical blocking agent may reduce water influx into the wellbore, resulting in increased hydrocarbon production rates and ultimately increasing the recoverable reserves.
Typically, such chemical blocking agents are comprised of a gel such as a polymer gel or a gelatinous foam. However, the selective placement of these chemical blocking agents in the desired areas of the formation has been problematic. For instance, the placement of the chemical blocking agent by gas injection typically results in poor placement due to overriding of the gas or fingering of the gas through the blocking agent during the gas injection process. Accordingly, the effectiveness of the gas injection process for properly placing the chemical blocking agent is reduced. None of the available methods for the placement of the chemical blocking agent downhole have been found to be fully satisfactory.
For instance, U.S. Pat. No. 4,694,906 issued Sep. 27, 1987 to Hutchins et. al. describes a method for placing a gelatinous foam downhole in order to block or plug higher permeability zones of the formation to enhance gas flooding recovery operations. In particular, an aqueous liquid solution and a foam emplacement gas are injected through the wellbore into the formation. Upon contact of the aqueous solution with the foam emplacement gas within the reservoir, a thickened or gelatinous foam plug is formed. The foam plug therefore possesses the properties of both foams and gels and is comprised of a gelatinous stable foam having stiffened foam films of crosslinked polymer which resists collapse.
U.S. Pat. No. 5,203,834 issued Apr. 20, 1993 to Hutchins et. al. describes a method including the injection into the formation of a composition capable of forming a foamed gel and a gas. The composition comprises an ingredient capable of transforming the composition into a gel, a surfactant and a delayed gel degrading agent. The composition and gas interact, forming a foamed gel. The delayed gel degrading agent subsequently creates pathways in the foamed gel by connecting the bubbles present in the gel. The pathways preferentially enhance the flow of hydrocarbons, as compared with water, through the foamed gel.
U.S. Pat. No. 5,462,390 issued Oct. 31, 1995 to Sydansk describes a process for blocking fluid flow in a soil, and more particularly, for placing a foamed gel in a soil to reduce the flow capacity of the soil to a migratory fluid. The process is provided for “near-surface” soil treatment and comprises the generation of a foamed gel from a gelation solution and gas. The foamed gel may be pre-formed at the surface, by pre-mixing the gelation solution and the gas, prior to placement in the soil. Alternately, the gas may be added to the gelation solution after the injection of the gelation solution in the soil in order to generate the foamed gel in situ. Therefore, placement and generation of the foamed gel occur simultaneously. Finally, the gelation solution and the gas may be co-injected. U.S. Pat. No. 6,103,772 issued Aug. 15, 2000 to Sydansk describes a similar process for use in a subterranean hydrocarbon bearing formation.
As indicated, although known methods for the placement of chemical blocking agents in the formation have some amount of success, there remains a need for an improved method of reducing water influx into a wellbore in fluid communication with a subterranean formation. Further, there remains a need for an improved method for placing a chemical blocking agent in a desired position in order to thereby reduce the influx of water.